title: Beetroot juice supplementation speeds O2 uptake kinetics and improves exercise tolerance during severe-intensity exercise initiated from an elevated metabolic rate.
abstract: Recent research has suggested that dietary nitrate (NO3(-)) supplementation might alter the physiological responses to exercise via specific effects on type II muscle. Severe-intensity exercise initiated from an elevated metabolic rate would be expected to enhance the proportional activation of higher-order (type II) muscle fibers. The purpose of this study was, therefore, to test the hypothesis that, compared with placebo (PL), NO3(-)-rich beetroot juice (BR) supplementation would speed the phase II VO2 kinetics (τ(p)) and enhance exercise tolerance during severe-intensity exercise initiated from a baseline of moderate-intensity exercise. Nine healthy, physically active subjects were assigned in a randomized, double-blind, crossover design to receive BR (140 ml/day, containing ~8 mmol of NO3(-)) and PL (140 ml/day, containing ~0.003 mmol of NO3(-)) for 6 days. On days 4, 5, and 6 of the supplementation periods, subjects completed a double-step exercise protocol that included transitions from unloaded to moderate-intensity exercise (U→M) followed immediately by moderate to severe-intensity exercise (M→S). Compared with PL, BR elevated resting plasma nitrite concentration (PL: 65 ± 32 vs. BR: 348 ± 170 nM, P < 0.01) and reduced the VO2 τ(p) in M→S (PL: 46 ± 13 vs. BR: 36 ± 10 s, P < 0.05) but not U→M (PL: 25 ± 4 vs. BR: 27 ± 6 s, P > 0.05). During M→S exercise, the faster VO2 kinetics coincided with faster near-infrared spectroscopy-derived muscle [deoxyhemoglobin] kinetics (τ; PL: 20 ± 9 vs. BR: 10 ± 3 s, P < 0.05) and a 22% greater time-to-task failure (PL: 521 ± 158 vs. BR: 635 ± 258 s, P < 0.05). Dietary supplementation with NO3(-)-rich BR juice speeds VO2 kinetics and enhances exercise tolerance during severe-intensity exercise when initiated from an elevated metabolic rate.
authors.affiliation: Sport and Exercise Physiology Research Team, Liverpool Hope University, Liverpool, United Kingdom;
authors.forename: Brynmor C
authors.initials: BC
authors.lastname: Breese
authors.forename: Melitta A
authors.initials: MA
authors.lastname: McNarry
authors.forename: Simon
authors.initials: S
authors.lastname: Marwood
authors.forename: Jamie R
authors.initials: JR
authors.lastname: Blackwell
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Bailey
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Jones
mesh_terms: D000328:Adult; D001481:Basal Metabolism / Q000187:drug effects / Q000502:physiology; D027461:Beta vulgaris; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D004734:Energy Metabolism / Q000187:drug effects* / Q000502:physiology; D017079:Exercise Tolerance / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D009566:Nitrates / Q000494:pharmacology*; D009573:Nitrites / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D010807:Physical Endurance / Q000187:drug effects / Q000502:physiology; D010936:Plant Extracts / Q000494:pharmacology*; D018517:Plant Roots
chemical_list: D007773:Lactates; D009566:Nitrates; D009573:Nitrites; D010936:Plant Extracts
keywords: fatigue; motor unit recruitment; muscle oxygenation; nitric oxide; phase II time constant